Of the professors then at Heidelberg, Leuckart, the zoologist, was, perhaps, the most inspiriting. His lectures were full of original suggestions and clever hypotheses, which excited and sometimes amused his listeners. He knew how to take advantage of the enthusiasm of his brighter pupils, and, at their request, gave them a separate course of instruction on special groups of animals; not without some personal sacrifice, for these extra lectures were given at seven o'clock in the morning, and the students were often obliged to pull their professor out of bed for the purpose. The fact that they did so shows at least the friendly relation existing between teacher and scholars. With Bischoff the botanist also, the young friends were admitted to the most kindly intercourse. Many a pleasant botanical excursion they had with him, and they owed to him a thorough and skillful instruction in the use of the microscope, handled by him like a master. Tiedemann's lectures were very learned, and Agassiz always spoke of his old teacher in comparative anatomy and physiology with affectionate respect and admiration. He was not, however, an inspiring teacher, and though an excellent friend to the students, they had no such intimate personal relations with him as with Leuckart and Bischoff. From Bronn, the paleontologist, they received an immense amount of special information, but his instruction was minute in details rather than suggestive in ideas; and they were glad when their professor, finding that the course must be shortened for want of time, displayed to them his magnificent collection of fossils, and with the help of the specimens, developed his subject in a more general and practical way.* (* This collection was purchased in 1859 by the Museum of Comparative Zoology in Cambridge, Massachusetts, and Agassiz had thus the pleasure of teaching his American pupils from the very collection in which he had himself made his first important paleontological studies.) Of the medical professors, Nageli was the more interesting, though the reputation of Chelius brought him a larger audience. If there was however any lack of stimulus in the lecture rooms, the young friends made good the deficiency by their own indefatigable and intelligent study of nature, seeking to satisfy their craving for knowledge by every means within their reach.* (* The material for this account of the student life of the two friends at Heidelberg and of their teachers was chiefly furnished by Alexander Braun himself at the close of his own life, after the death of Agassiz. The later sketches of the Professors at Munich in 1832 were drawn in great part from the same source.)